Generally, the process of electrostatographic printing is executed by exposing a light image of an original document onto a substantially uniformly charged photoconductive member. Exposing the charged photoconductive member to a light image discharges the photoconductive surface thereon in areas corresponding to non-image areas in the original document while maintaining the charge in image areas, thereby creating an electrostatic latent image of the original document on the photoconductive member. Toner particles are subsequently deposited onto the latent image to form a toner powder image. This toner powder image is then transferred from the photoconductive member, either directly or after an intermediate transfer step, to a final support sheet. The transferred image may then be permanently fused to the sheet. In a final step, the photoconductive surface of the photoconductive member is cleaned to remove any residual developing material thereon in preparation for successive imaging cycles.
This printing process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrostatographic printing applications such as, for example, ionographic printing and reproduction, where charge is deposited on a charge retentive surface in response to electronically generated or stored images. A laser beam may also be used to imagewise discharge the photoconductive member in accordance with stored electronic information.
The process of transferring toner particles from the photoconductive surface is realized at a transfer station. In a typical transfer station, transfer is achieved by applying electrostatic force fields in a transfer region sufficient to attract the toner particles from the photoconductive surface to the final support sheet or an intermediate transfer belt.
Intermediate transfer belts are used in conjunction with one (tandem) or more (non-tandem) photoconductive members for transport of a developed toner powder image to a final support sheet. For example, intermediate transfer belts are used in non-tandem applications where successive color toner powder images are individually transferred to the transfer belt where they are sequentially superimposed onto the previously transferred color toner powder image. A composite image is formed and then transferred from the transfer belt to a final support sheet. Alternatively, the composite image may be formed on the photoconductor before being transferred to an intermediate transfer belt, and then to a final support sheet. In a tandem apparatus, each of multiple photoconductive members transfers an individual color toner powder image to the intermediate transfer belt in sequential superimposed registration onto the previous color toner powder image, thereby forming a full composite image on the intermediate transfer belt.
Transfer of developed toner images between support surfaces is often accomplished by using a corona generating device. The intermediate transfer member or final support sheet, is placed in direct contact with the developed toner image on the photoconductive surface. The corona generator sprays the intermediate member or final support sheet with ions having a polarity opposite that of the toner particles, thereby transferring the toner particles from the photoconductive surface to the intermediate member or final support sheet.
Alternatively, transfer can be induced by applying a potential difference between the intermediate member or final support sheet by a biased member contacting therewith. For example, a biased transfer roll system (BTR) defines a nip with the photoconductor through which the intermediate member or final support sheet passes. The pressure and electrical field in the nip transfers the toner image from the photoconductor to the intermediate member or final support sheet.
An electrostatic transport belt is commonly used in conjunction with a corona generator. Generally, an electrostatic transport belt transports the final support sheet into and out of contact with the photoconductor at a transfer station. A corona generator for accomplishing transfer, is located behind the electrostatic transport belt. U.S. Pat. No. 3,966,199 to Silverberg discloses such a system, the relevant portions of which are hereby incorporated herein by reference. Transfer could alternatively be accomplished with a biased transfer roller, rather than a corona generator, positioned against the back side of the electrostatic transport belt.
Thus, transfer support members such as those hereinbefore described, (e.g. bias transfer roll, intermediate transfer belt, electrostatic transport belt), have in common their function of directly supporting the transfer of a developed toner powder image from a photoconductive member. Due to the varying electrostatic force fields involved in the transfer process, stray toner and debris particles may adhere to the surface of the transfer support member. Consequently, there is a need to clean the surface of the transfer support member so as to prevent degradation of the quality of subsequent copies and/or prevent toner particles from being fused to the backside of the final support sheet. Typical cleaning methods include wiping with a brush, a web, a blade and the like, a magnetic brush, air flow, or a combination of these. All of these, alone or in combination, require that collected residual toner and debris be removed from the cleaning device.
Thus, it is necessary to clean this residual material from the transfer support member surface with a cleaning system separate from the cleaning system used to clean the photoconductor.
The following disclosures may be relevant to various aspects of the present invention.
U.S. Pat. No. 3,781,105 to Meagher discloses a biasing transfer roller for electrostatic transfer of charged particles to a transfer member using constant current control of the bias voltage supply in a transfer roller system, rather than constant voltage control. A cleaning brush with its associated vacuum housing is described as positioned adjacent to the bias transfer roller to clean stray toner and dirt from the outer surface of the roller.
U.S. Pat. No. 5,214,479 to Lindblad et al. discloses a cleaning apparatus for cleaning residual toner and paper fiber residue from a biased transfer roll using high velocity air and substantially contactless flexible biased conductive shims. The air flow created evacuates the air with debris particles therein through a vacuum chamber, where a filter collects the residue which is then deposited in a filter bag.
U.S. Pat. No. 5,237,374 to Ueno et al. discloses a second cleaning blade for cleaning residual toner from the intermediate transfer body, with a contact pressure applied to the intermediate transfer body being larger than that applied by a first cleaning blade to the photoconductive body.
U.S. Pat. No. 4,588,279 to Fukuchi et al. discloses a cleaning roller rotating in contact with an intermediate transfer member, wherein the cleaning roller uses a structure such that the outer layer consists of a porous or fibrous substrate and is covered with toner or a resin identical or compatible with the toner. The toner sticking to the cleaning roller member is removed by being scraped by a blade at a stage when it has become substantially hardened on the roller. Periodic replacement of the cleaning roller is also described as an option for removal of accumulated toner.
U.S. Pat. No. 4,788,572 to Slayton et al. discloses a transfer belt which rotates with photoconductor belt whereby a cleaning knife disengages with the transfer belt during the cycles when toner is building an image onto the intermediate transfer belt, and engages with the transfer belt after the toner image has been transferred from the transfer belt, for removal of residual toner. The cleaning knife disengages with the transfer belt at a defined seam area so that the "streak" of toner from disengaging action is left on the transfer belt outside of the imaging area of the photoconductor belt. Slayton et al. describes a receptacle bin for collection of residual toner particles scraped from the transfer belt by the knife, which fall into the receptacle by gravity.
U.S. Pat. No. 5,253,023 to Hosaka et al. may also be found to be relevant to the present invention. Hosaka discloses an electrostatographic apparatus wherein transferring and fixing of the toner image onto a transfer material is performed simultaneously using a heating means and a soft roller transfer unit. In the developer unit an AC voltage is superimposed over a DC voltage so that development of the current image formation, accomplished by the DC voltage, occurs at the same time as removal of the residual toner created during the previous image formation, which is accomplished by the AC voltage. When improper feeding of the recording sheet occurs, Hosaka et al. describes applying a reverse bias voltage to the transfer roller while operating the recording machine in an opposite direction, to allow toner that attaches to the transfer roller to return back to the photosensitive drum.